Eucaliptus chip compaction disturbance

Eucalyptus Chip Compaction Disturbance Analysis in a Vapor Phase Continuous Digester.
CORREIA, F.M.(1) ; COLODETTE, J.L. (2); REGAZZI, A. J. (2) ; GOMIDE, J.L. (2)

1) – CENIBRA CELULOSE NIPO BRASILEIRA SA [e-mail] 2) – UFV UNIVERSIDADE FEDERAL DE VIÇOSA

ABSTRACT

Digesters are complex reactors, where the delignification of wood chips takes place through combined chemical treatment and thermal effects. One of the main variables that characterize the quality of the produced pulp is the kappa number, which represents the amount of residual lignin in the pulp. Besides the influence from the wood chip quality, temperature and alkali, the kappa number is strongly influenced by the residence time of chips in the digester. Therefore, there is a close relationship between the compaction of chips and their residence time in the vessel. In addition, the compaction of the chips closely relates to the kappa number, the production rate, the chip level, and the dilution factor.
One of the most difficult operational problem for the digester control is to stabilize the vertical movement of chip bed. The abnormal hydraulic column movement directly determines the residence time for the chips, reflecting the difficulties of controlling the level of chips and liquor.
Published papers of several authors, have already demonstrated the relationships between the different process variables and their reactions to chemical kinetics, developing different models of cooking reactions. However, such models are applicable only to digester equilibrium conditions. A major operation issue at the continuous digester operation is the appropriate chip level control. If present problems in the chip compaction bed, affecting chip level, the reaction time becomes out of control. Significant effects occurs on the production, quality and uniformity product as result.
There are several possible causes of chips compaction